Water tube boiler



Sept. 4, 1934.- F. WEMPE. 1,972,504

Patented Sept. 4, 1934 UNITED STAT 1,972,504 WATER TUBE BOILER Friedrich Wempe, Kassel-Wilhelmshohe. Ger- \many, assignor to Schmidtsche Heissdampl'- Gesellschaft Germany 1n. b. H., Kassel-Wilhelmshohe,

Application February 24, 1933, lSerial No. 658,319 In Germany March 2, 1932 Claims. (Cl. 122-265) In the case of water tube boilers having a water circulation through risers forming the part of the bank lying nearer to the furnace and downcorners forming lthe part of the bank more remote from the furnace there are, as is well known, tubes in the intermediate region between the two groups .in which circulation is defective these tubes becoming risers or downcomers depending upon the load on the boiler.- In order to minimize the danger cf corrosion in these tubes, it has been suggested in the past to place them so that they are swept only by gases which have a relatively low temperature. It is, however, not always easy to adopt such an arrangement, and in addition even when it is adopted there is no absolute guarantee that it will entirely prevent corrosion. The present invention adopts a different method, namely that the circulation shall always be in the same direction in all tubes of the bank so that there will be no tubes in which the circulation is stagnant. For this purpose the invention proposes to arrange in advance of the downcomers separate risers having enlarged heating surface as compared with the surface of the risers ahead of them and with the downcomers. In these risers with increased heat absorbing surface, the Aproportion of. steam in the steam and water mixture is increased because of the greater rate of heat absorption and this assures a rapid upward ow in these tubes. The tubes following these special risers in the direction of gas ow have only the normal heating surface and because of their relatively small heat absorption are certain to act as downcomers. The invention therefore makes it possible to have a perfectly definite line of demarcation at the desired point in the heated water tube bank between the risers and downcomers.

In the drawing, means of carrying out the invention are illustrated.

Fig. 1 is a vertical section through a semiverticalwater tube boiler. Fig. 2 shows a variation in a similar boiler. Fig. 3 is a cross section on line 3 3 of Fig. 2, and Fig. 4 shows a further variation in a similar boiler.

The semi-vertical tube boiler of Fig. 1 is a marine boiler of the well known A-type. .It has two lower drums 1--1, an upper drum 2, and two banks of tubes 3-3 arranged in the shape of a roof over the furnace. The gases of combustion flowing toward the stack connection 4 iiow across the tube banks in a direction generally transverse tothe tubes. 5 designates the risers lying in the front portion of the tube bank and therefore 55 touched first by the hot gases, while 6 designates the downcomers forming the farther portion of the bank as regards the gas flow. The risers 5 and the downcomers 6 are formed by smooth tubes, straight for the major portion of their lengths. In accordance with the invention there is arranged between the two groups 5 and 6 0f each bank a row of zig-zag tubes 7 whose heat absorbing surface is materially larger than that of the tubes 5 and 6. Although the temperature of the gases has already been lowered by their giving up heat to the risers 5 when they arrive at the tubes 7, nevertheless these tubes can on ac' count of their increased heating surface still absorb a relatively large amount of heat. Asa consequence there is still a rapid vaporization in 7 the vtubes 7 so that the proportionate part of steam in the steam and water mixture in these tubes is relatively large. The downcomers 6 following the tubes 7 have in comparison with the tubes 7 a small heat absorbing surface. In addition, the heating gases have been considerably cooled when they reach these tubes. The steam generation in lrhe downcomers 6 is therefore so small that it uoes not interfere with the downward flow in these tubes'. Just as in the risers 5 and 7, a unidirectional water circulation is therefore also assured in the downcomers 6. There are no tubes in the bank in this new form of boiler with indeterminate or stagnant circulation.

In the form of the invention shown in Fig. 2 85 there are inserted between the risers 5 at the front and the downcomers 6 at the rear, two rows of tubes 8 and 9 having an enlarged heat absorbing surface. Different from the form of Fig. 1, the increase in the heating surface in this case is not obtained by giving these tubes a zig- ,zag form but by providing them with external ribs and flanges. The tubes 8 are provided with longitudinal flanges 10 and the tubes 9 with circumferential ribs 12. As far as carrying out the 95 invention is concerned, it is immaterial which of these means is utilized to increase the heat o absorbing surface of these special risers. The action of this arrangement and particularly the action of the special tubes with increased heat absorbing surface is obviously the same as that pointed out in connection with the form of Fig. 1 above.

In the illustrative example of Fig. 4 only the first two rows of risers 5 which will .absorb heat 105 both by radiation from the furnace'and convection from the gases passing through the bank, and the downcomers 6 at the rear of the bank are given the shape of smooth generally straight tubes. The rows of tubes 13, 14 and 15 lying 110 radiantly heated evaporating tubes, extending vertically below the lower drumvand lining the .nace so that the rear rowof risers` 15 has the greatest amount of heat absorbing surface. this gradual increase of heating surface, the effect of the gradual decrease in temperature of the heating gases is at least in part counteracted and asteam and water mixture is obtained in each of these 'rows composed of approximately the same percentage of steam and water.

It may be mentioned that it is old-to connect furnace wall below it, into thel lower drum of a semi-vertical tube boiler and to lead the steam and Water mixture coming from them through a conducting means to the tubes of the bank which receive the least amount of heat. This is done to avoid the mixture in the front rows of thel bank having too much steam in it thereby endangering these tubes by overheating. The present invention has nothing in common with such an arrangement since in such vertical banks there are no downcomers at all, but all of the tubes of the bank act as risers and large unheated downcomers `are employed.

Contrasted with this the present invention always has a portionofthe heated tubes, of the bank'forming downcorners and the invention has for'its purpose to effect a deiinite division for all conditions of operation between the-risers and downcomers of the heated bank of tubes.

While the invention hasbeendescribed, in .the

above in connection with a single type of boiler,

it will be obvious that it is not limited in this respectbut can be utilized in connection withv various types of water tube boilers. The appended l claimsare intended to cover this as well as Aother 40 variationswhich may be made in practicing the invention. i y

WhatI claim is: n 1. In a boiler, a bank of tubes heated by the products of combustion passing through the bank on their way from the furnace to the stack in a direction generally transverse to the bank, that portion of the tubes of the bank nearer the furnace acting as risers'and the remaining ones as downcomers, those of the riser tubes with which the gases come in contact last having a greater Y external heat-absorbing `surface than the other risers.

2. In a boiler, a` bank of tubes heated by the products of combustion passing through the bank on their way from the furnace to the stack in a direction generally transverse to the bank, that nace acting as risers and the remaining ones as downcomers, those of the riser tubes with which the gases come in contact last having a greater 'external' heat-absorbing surface than the downcomers with whichr the gases come in contact next after leaving the risers.

3. In a boiler, a, bank of tubes heated by the products of combustion passing through the bank on their way from the furnace to the stack in a direction generally transverse to the bank, that portion' of the tubes of the bank nearer the furnace acting as risers and the remaining ones as downcomers, those of the riser tubes with which the gases come 'in contact last having a greater external heat-absorbing surface than any of downc'omers. I

4. In a boiler, a bank of tubes heated by the products of combustion passing through the bank on their way from the furnace to the stack in a direction generally transverse tothe bank. that portion ofthe tubes of the bank nearer thefurther I `portion of the tubes of the bank nearer the fury nace acting as risers and the vremaining ones as downcomers, those ofthe riser tubes with which ythe gases come in contact. last having a greater external heat-absorbing surface.

ythan vthe other risers or the downcomers.

. l 5. In a boiler, a bank of tubes heatedby theV nace acting as risers and the remaining ones as 5 downcomers, the risers comprising a plurality of rows successively touched by the gases, the tubes 

